Expressions and Variables: Evaluating Two Variables

-  To evaluate an algebraic expression, substitute a number for each variable.
-  Perform the arithmetic operations to find the value of the expression.

Examples:
Example 1.  Calculate this expression for and .
Solution: First, substitute for , and for .
Then:
Now, use order of operation to find the answer:

Example 2.  Evaluate this expression for and . 
Solution: Substitute for , and for .
Then:

Example 3.  Find the value of this expression, when and .
Solution: Substitute for , and for .
Then:

Example 4.  Evaluate this expression.
Solution: Substitute for , and for and simplify.
Then: